Stacking refers to combining at least two switch devices to work together to provide as many ports as possible in a limited space. The switch devices supporting stacking are interconnected to form a combined device, which is called a stack. Each of the switch devices forming the stack is called a member. When the members form the stack, these members become one entity whether in management or in use. In other words, the members forming the stack can be managed and used as a single device so that the number of ports and switching capacity can be increased by adding a device. In addition, the reliability of the whole stack is also improved through backup among the members.